text: *14 January 2020 Michigan Attorney General Dana Nessel filed a lawsuit against 17 companies, including 3M, Chemours, and DuPont, for hiding known health and environmental risks from the state and its residents. Nessel's complaint identifies 37 sites with known contamination
  *10 March 2020 EPA announced its proposed regulatory determinations for two PFAS in drinking water. In a Federal Register notice the agency requested public comment on whether it should set maximum contaminant levels for PFOA and PFOS in public water systems.
  *3 August 2020 The Michigan Department of Environment, Great Lakes, and Energy (EGLE, formerly MDEQ) enacts some of the strictest drinking water standards in the country in the form of maximum contaminant levels (MCLs), limiting PFOA at 8 ppt and PFOS at 16 ppt (lowered from the previous limit of 70 ppt for both), and introduces MCLs for 5 previously unregulated PFAS compounds – PFNA at 6 ppt, PFHxA at 400,000 ppt, PFHxS at 51 ppt, PFBS at 420 ppt, and HFPO-DA at 370 ppt. The passage of these contaminant levels marks the first time Michigan has developed its own MCLs rather than adopting or modifying existing federal standards.
  *3 March 2021 EPA announced that it will develop national drinking water standards for PFOA and PFOS.
  *17 March 2021 EPA announced plans to revise wastewater standards (effluent guidelines) for manufacturers of PFAS chemicals.
  *21 April 2021 3M sues the state of Michigan, seeking to invalidate its new drinking water standards.
  *July 2021 The Michigan Department of Health and Human Services (MDHHS) updated its Do Not Eat advisory for white-tailed deer at Clarks Marsh (near former WAFB) from 5 to 3 miles. After testing an additional 44 deer near Clarks Marsh MDHHS was able to identify a relationship between PFOS detections in deer liver with the deers distance from Clarks Marsh. The Michigan DNR estimated a 3-mile area as the expected travel range of white-tailed deer in the area. In both muscle and liver samples, the highest level of PFAS chemical was PFOS, at 82.6 parts per billion (ppb) in a muscle sample and 2,970 ppb in a liver sample.
  *14 September 2021 EPA announced plans to revise effluent guidelines for businesses that conduct chromium electroplating operations and discharge PFAS in their wastewater.
  *21 October 2021 EPA announced, "a whole-of-agency approach" for addressing PFAS, titled "PFAS Strategic Roadmap: EPA's Commitments to Action 2021-2024".
  *27 December 2021 EPA published a regulation requiring drinking water utilities to conduct monitoring for 29 PFAS compounds. The data are to be collected during 2023 to 2025. The agency may use the monitoring data to develop additional regulations.
  *13 April 2022 14 State Attorneys General signed a letter to the EPA urging the agency to use its current-year funding to "meet commitments and deadlines outlined in its PFAS Strategic Roadmap".
  *15 June 2022 The EPA issued interim updated drinking water health advisories for PFOS and PFOA, drastically lowering previous levels from 70 ppt for both to 0.02 ppt for PFOS and 0.004 ppt for PFOA.  The agency also issued final health advisories for HFPO-DA and its ammonium salt GenX at 10 ppt and for PFBS at 2000 ppt.
  *22 June 2023 the American multinational 3M reached a $10.3bn settlement with a host of US public water systems to resolve water pollution claims tied to PFASs. Three other major chemicals companies – Chemours, DuPont and Corteva – have reached an agreement in principle for $1.19bn to settle claims they contaminated US public water systems with PFAS.